fixup: update the documentation

Mention the change in the release notes and extend the attribute
descriptions.

Author: a-nogikh

clang/docs/ReleaseNotes.rst

@@ -327,6 +327,10 @@ Attribute Changes in Clang
 - New format attributes ``gnu_printf``, ``gnu_scanf``, ``gnu_strftime`` and ``gnu_strfmon`` are added
   as aliases for ``printf``, ``scanf``, ``strftime`` and ``strfmon``. (#GH16219)
 
+- The malloc attribute can now be applied to functions returning span-like structures (structs
+  containing a pointer field and a size integer field). Currently, this is primarily used for
+  Allocation Token instrumentation.
+
 Improvements to Clang's diagnostics
 -----------------------------------
 - Diagnostics messages now refer to ``structured binding`` instead of ``decomposition``,

clang/include/clang/Basic/AttrDocs.td

@@ -5244,6 +5244,11 @@ deallocation function. When this form is used, it enables the compiler to
 diagnose when the incorrect deallocation function is used with this variable.
 However the associated warning, spelled `-Wmismatched-dealloc` in GCC, is not
 yet implemented in clang.
+
+It's also possible to place the ``malloc`` attribute on the functions returning
+span-like structures, that is, the structs having a pointer as the first field
+and an integer with the size of the actually allocated memory as the second field.
+Note that extended semantics is clang-specific and not currently supported in GCC.
   }];
 }